Stable uv laser

ABSTRACT

UV laser devices, systems, and methods are shown and/or described herein. Included are a method, device or system for VECSEL and MECSEL lasers including both barrier-pumped and in-well pumped lasers. Also disclosed is a method of manufacturing gain chips for use in the lasers, arrangements of lasers, and selection of proper non-linear crystal (NLC) for use in the device.

BACKGROUND

The present developments relate to an apparatus and method to generatetemporally stable ultra violet (UV) light. In many implementations,these may particularly include and/or be directed to methods, systemsand/or devices which may use a Semiconductor Thin Disc Laser (STDL) as aVisible Wavelength Laser Light Source (VWLS) and a frequency doublingoptics component, such as a Non-Linear Crystal (NLC) or a periodicallypoled material, to convert the visible light into UV light.

The apparatuses and/or methods that will provide for temporally stableUV light may be used in a variety of applications including but notlimited to scanning, spectroscopy/spectrometry, telecommunicationapplications, and/or medical applications. UV lasers may be well suitedfor applications on a micro scale that require high quality results.Moreover, UV lasers may be utilized in a variety of commercial andindustrial applications, including, but not limited to: machining on amicro-scale, engraving of precision tools for stamping or micro-sparkerosion, marking of glass and synthetics whereby the surface is notchanged in structure or chemical composition, drilling of small holes ina variety of materials for example diesel injectors, and precisioncleaning of surfaces, such as with artwork. These examples andapplications of UV lasers are non-limiting examples, as there are myriadapplications and uses of UV lasers.

Several possible/optional desiderata for further options of generationof temporally stable high intensity visible light, such as from VerticalExternal Cavity Surface Emitting Laser(s) (VECSELs) or from MembraneExternal Cavity Surface Emitting Laser(s) (MECSELs) are describedherein. Furthermore, several possible/optional implementations andarrangements related to one or more quantum wells (QWs) or one or moreQuantum Dots (QDs), formation and manufacture of QWs, QDs,barrier-pumped lasers, in-well pumped lasers, and cooling of QWs/QDs arealso provided. Additionally, several implementations and selectionsrelated to the material and length of NLCs are also evident anddescribed.

SUMMARY

UV or frequency up converted laser devices, systems, and/or methods areshown and/or described herein. Included are methods, devices, and/orsystems for using a STDL (Semiconductor Thin Disc Laser) as a VWLS(Visible Wavelength Laser Light Source) and a frequency doubling opticscomponent, such as a Non-Linear Crystal (NLC) or a periodically poledmaterial to convert the visible light into UV light. As furtherdescribed herein, the STDL is electrically or optically pumped togenerate the visible laser light. Visible Wavelength Light (VWL) is alsoreferred to herein as visible or VISible light (aka VIS), also anintermediate output that when directed through an NLC can yield a finalUV output.

VECSEL based UV lasers are provided and may include a VECSEL quantumwell (VECSEL QW or QW) or QD gain chip, a birefringent filter plate(BFP) and/or Etalon, a non-linear crystal (NLC) and one or more mirrors,e.g., cavity mirrors. The VECSEL gain chip when electrically oroptically pumped produces a laser photon or output. This laser photontravels on an optical path through a BFP and contacts a first cavitymirror. The first mirror reflects the laser photon or VWL through an NLCcrystal of proper length and material to convert the VWL (VisibleWavelength Light, also known as VIS) into stable UV light. The secondmirror which is positioned nearly parallel to the first mirror but onthe opposite side of the NLC then reflects the stable UV light backtoward the first mirror and eventually toward a target outside thecavity.

MECSEL based UV lasers are also provided and include similar structuresas the VECSEL described above; however, the MECSEL is able to utilize athird mirror as the MECSEL is centrally located, whereas a VECSEL isterminally or externally located.

Implementations of the VECSEL QW or QD gain chip and the MECSEL QW or QDgain chip are described. The gain chips may be assembled under specificconditions to ensure proper optical bonding is achieved between andamong each of the layers of the respective VECSEL QW or QD and MECSEL QWor QD gain chips. The layers and arrangement of heat spreaders arediscussed as these provide for proper cooling during high poweroperation.

In other features, laser systems that employ barrier-pumping and in-wellpumping are described. These two techniques and setups may have certainfeatures that may in some instances be employed in some preferredimplementations of the developments hereof.

BRIEF DESCRIPTION OF DRAWINGS

For a detailed description of exemplary implementations of thedevelopments, reference will now be made to the accompanying drawings inwhich:

FIG. 1A shows a schematic overview of a VECSEL in accordance with atleast some implementations hereof;

FIG. 1B shows a schematic overview of a MECSEL in accordance with aleast some implementations hereof;

FIG. 2 provides a sectional view of the layers of a quantum well (QW) orQD of a VECSEL gain chip (not to scale), hereof;

FIG. 3 provides a sectional view of the layers of a gain region of aquantum well (QW) or QD of a MECSEL gain chip (not to scale) hereof;

FIG. 4 provides a sectional view of the layers of a gain region of aquantum well (QW) of a MECSEL using SiC as heat spreaders (not to scale)hereof;

FIG. 5A provides an exemplary pattern related to forming of wafers forVECSELs and/or MECSELs hereof;

FIG. 5B shows an exemplary pattern for laser scribing and breaking toform single gain chips for VECSELs and/or MECSELs hereof;

FIG. 6 provides a graph of reflectivity versus the thickness of a thinfilm that may be placed between a QW and an SiC wafer;

FIG. 7 shows a schematic overview of a MECSEL where a gain chip isplaced at the Brewster's angle relative to the optical path;

FIG. 8 provides a graph that demonstrates the relative intensity versusthe wavelength (bandwidth and UV conversion efficiency) for twoNon-Linear Crystals (NLCs) lengths under similar Visible WavelengthLaser Light Source (VWLS) conditions;

FIG. 9 provides a graph of Full Width at Half Maxima (FWHM) plottedversus Periodically Poled Stoichiometric Lithium Tantalate (PPSLT)length;

FIG. 10 provides a schematic overview of a basic UV laser using VECSELin accordance with at least some implementations hereof;

FIG. 11 provides a schematic overview of a UV laser using VECSEL inaccordance with at least some implementations hereof;

FIG. 12 provides a schematic overview of a UV laser using MECSEL inaccordance with at least some implementations hereof;

FIG. 13 provides a schematic overview of a walk-off compensated NLC inaccordance with at least some implementations hereof;

FIG. 14 provides a schematic overview of an electrically or opticallypumped VECSEL hereof;

FIG. 15 shows a schematic overview of an in-well pumped MECSEL in astraight cavity hereof;

FIG. 16 provides a schematic overview of some alternative additionaloptics and distances of an exemplary VECSEL, in accordance with at leastsome implementations hereof;

FIG. 17 provides a schematic overview of a MECSEL in a V-shaped cavitywith an in-well pumping layout;

FIG. 18A provides a side view of a valence band and conduction band ofthe quantum well of an exemplar gain chip hereof;

FIG. 18B provides a side view of a barrier-pumped laser hereof;

FIG. 18C provides a side view of an in-well pumped laser hereof;

FIG. 19A provides a side view schematic diagram of an alternativebarrier-pumped laser hereof; and

FIG. 19B provides a side view schematic diagram of an alternativein-well pumped laser hereof.

DETAILED DESCRIPTION

The following discussion is directed to various implementations of thedevelopments hereof. Although one or more of these implementations maybe preferred, the implementations disclosed should not be interpreted,or otherwise used, as or for limiting the scope of the disclosure,including the claims. In addition, one skilled in the art willunderstand that the following description has broad applications, andthe discussion of any implementation is meant only to exemplary of thatimplementation and is not intended to intimate that the scope of thedisclosure, including the claims, is limited to that implementation.

Various example implementations are directed to UV lasers, and moreparticularly to UV lasers that may provide for the efficient andtemporally stable generation of UV light from a Visible Wavelength LaserLight Source (VWLS), by using a laser cavity supporting multiplefrequencies of VWLS and using length optimized non-linear optics todouble the visible frequencies inside the laser cavity into UV light.The specification first turns to a high-level overview of UV lasers inexample systems.

As a first note, to achieve visible light to UV conversion there are twoelements that may need to be met: (1) temporally stable high intensityof visible light, and (2) a proper non-linear crystal, or periodicallypoled material to convert the visible light into UV light.

FIG. 1A shows a simplified schematic overview of a VIS laser 100 (partof the UV laser), here a VECSEL 110, and FIG. 1B shows a simplifiedschematic overview of a VIS laser 100 (part of the UV laser), here aMECSEL 210, in accordance with example systems hereof. Myriad otherforms of UV or VIS lasers, whether alternative VECSELs or MECSELs, orotherwise, may fit within the scope hereof with no requirement to belimited to the implementations shown, whether in FIGS. 1A or 1B, orotherwise; limited only by the proper scope of the claims appendedhereto.

FIG. 1A shows a VECSEL 110 that has a VECSEL gain chip 150 that has oneor more quantum wells 120 (“QW” or “VECSEL QW” or a quantum dot, “QD”)which may then be the semiconductor gain media for the laser. The gainchip may include one or more laser cavities. The QW 120 may be disposedand/or enclosed inside a corresponding laser cavity, and a few watts ofvisible light power may, as a result of the enclosing, be extracted fromthe cavity by using one or more partial or fully reflecting cavitymirrors 130. The cavity mirror 130 can be a dielectric coated mirror orVolume Bragg Grating (VBG) mirror. VBG mirror can also serve aswavelength selecting and limiting device. The VECSEL QW 120 may thengenerate an output 140. Note, the output or light 140 is the VIS lightinside cavity mirrors 130; whereas the further outside output or light141 is the VIS output outside the cavity mirrors 130. Light intensityinside and outside has a ratio depending on the coating on mirrors 130and 230. The VECSEL QW 120 may be electrically or optically pumped forthe VECSEL QW 120 to produce an output 140. Between the cavity mirrors,the confined visible light 140 power intensity may be at least a factorof 10 or more than its power 141 outside of the cavity mirrors 130. Atypical enhancement factor is between 40 and 100 when all cavity mirrorsare highly reflective. Thus, a semiconductor thin disc laser cavity, andparticularly a VECSEL cavity may provide the necessary visible highintensity light 140 to provide the required temporally stable highintensity visible light 141 requisite for a UV laser.

Alternatively, FIG. 1B shows a UV or VIS laser 100 that may utilize aMECSEL 210 setup. Here, the MECSEL includes a MECSEL gain chip 250 thatfurther comprises MECSEL quantum wells 220 (“QW” or “MECSEL QW”) whichmay then be the semiconductor gain media for the laser. Like the VECSELsetup described above relative to FIG. 1A, the gain chip may include oneor more laser cavities. The QW 220 may be disposed and/or enclosedinside a corresponding laser cavity, and a few watts of visible lightpower may be extracted from the cavity by using one or more partial orfully reflecting cavity mirrors 230. The MECSEL QW 220 may beelectrically or optically pumped for the MECSEL QW 220 to produce anoutput 141. As mentioned above relative to FIG. 1A, the confined visiblelight 140 power intensity may be at least a factor of 10 or more thanits power outside of the cavity mirrors and typically an enhancementfactor between 40 and 100 may be achieved when all cavity mirrors arehighly reflective. In this way, a MECSEL cavity may provide thenecessary visible high intensity light 140 to provide the requiredtemporally stable high intensity visible light required for a UV laser.

The VECSEL QW of FIG. 1A and the MECSEL QW of FIG. 1B may require propercooling to ensure high power operation. In order to ensure propercooling of the QWs the gain region of both the VECSEL gain chip and theMECSEL gain chip a layered structure or layered arrangement may beemployed. In this technique, heat spreaders and reflectors withdesirable characteristics may be layered, or sandwiched, around the QWstructure.

Thus, FIG. 2 provides a sectional view of the layers of the gain region160 for the VECSEL gain chip 150. A heat spreader 170 may be the firstlayer of a VECSEL structure. The material, or composition, for the heatspreader 170 may be selected from diamond, SiC, or any high-thermalconducting optics can be used as/for a cooling device. In someinstances, using SiC instead of diamond as the heat spreader may providesome additional benefit as further discussed below in relation to FIG.4. In FIG. 2, the second layer is the VECSEL QW 120, and the third layeris a distributed bragg reflector (DBR) 172. One characteristic of theDBR is that the DBR may have high thermal resistance and thus will nothelp the cooling of the VECSEL as electrical or optical pumping powerincreases.

Further, FIG. 3 shows a sectional view of the layers of the gain region260 for the MECSEL gain chip 250. A heat spreader 170 may be the firstlayer of a MECSEL structure. Again, the material, or composition, forthe heat spreader 170 may be selected from diamond, SiC, or any highthermal conducting optics. In FIG. 3, the second layer is the MECSEL QW220, and the third layer is again a heat spreader 170. As shown, theMECSEL's QW layered structure does not have a DBR structure or layer;instead, the additional cooling is achieved by sandwiching the MECSEL QWstructure between two cooling devices, or heat spreaders.

As previously mentioned, using SiC as the heat spreader, instead ofdiamond or other materials, may provide some additional benefit becauseSiC has a coefficient of thermal expansion (CTE) that that is verysimilar to that of GaAs and of QW material. VECSELs and MECSELs areoften grown on gallium arsenide (GaAs) wafers and thus using SiC as aheat spreader may provide an efficient heat removal material. FIG. 4provides a sectional view of the gain region 260 for a MECSEL gain chip250. In this FIG. 4, the MECSEL QW 220 is sandwiched, or layered,between layers of SiC 174. As the pumping power increases, more wasteheat must be removed from the QW 220. In this implementation, SiC layers174 are used as efficient heat removal material. SiC has a CTE ofapproximately 4×10⁻⁶ /K which is closer to the QW's CTE (where wafer ismade from GaAs and QW is GaInP/AlGaInP/GaAs) which is approximately5×10⁻⁶ /K than diamond which has a CTE of approximately 1×10⁻⁶ /K. Athigher power operations, the temperature of the QW may rise as high as60° C. and a mismatch of CTE, like that of diamond, may cause the deviceto fracture or overheat and fail. Thus, SiC may avoid this problem asits CTE value is closer to that of GaAs/QW as used in the wafer of theQW.

In one implementation the subject matter hereof may provide for a methodof producing a VECSEL gain chip or a MECSEL gain chip, where the QWstructure is first grown on the desired substrate, or wafer, such asGaAs. The GaAs substrate typically may have a thickness of 0.2-0.5 mmdepending on the wafer diameter. After the QW is grown on the substratethe selected and/or specified heat spreader such as SiC is opticallybonded to the QW-GaAs wafer. Optical bonding involves one waferconforming to the other wafer to maintain good optical and thermalcontact. It is noted that, SiC is a hard material which is relativelystiff compared to GaAs which is relatively soft and in some instancesbrittle. Thus, in order to achieve optical bonding, it may beadvantageous to reduce the QW-GaAs wafer thickness from the GaAs side toaround 0.1 mm or less. This reduction in thickness makes the QW-GaAswafer more flexible. The SiC wafer and the thin, or reduced thickness,QW-GaAs wafer are surface activated and pressed together using a bondingprocess in a standard optical bonding machine such as EVP Group's EVG500series under high vacuum conditions, such as 10⁻⁷ torr or better. For aVECSEL QW gain chip, only one optical bonding is needed as one side ofthe VECSEL gain chip is covered by a DBR, as shown in FIG. 2.

For a MECSEL QW gain chip, after SiC-QW-GaAs becomes one single waferassembly, the assembly is dipped into acid solution such asH₂SO₄:H₂O₂:H₂O, or concentrated sulfuric acid, or NH₄OH:H₂O₂ to removethe GaAs selectively. Following this acid wash, only the thin QW layeris left on the SiC wafer. A second SiC wafer is then activated andpressed to the SiC-QW, utilizing the bonding process in a standardoptical bonding machine under high or ultra high vacuum conditions,described above. The result is the formation of a single SiC-QW-SiCwafer, as shown in FIGS. 3 and 4.

The SiC-QW-GaAs (VECSEL) wafer and the SiC-QW-SiC (MECSEL) wafer arefurther processed by applying an anti-reflection (AR) coating andmetallization with the pattern 180 as shown in FIG. 5A. The single, orindividual, SiC-QW-GaAs (VECSEL) gain chips, and the single, orindividual, SiC-QW-SiC (MECSEL) gain chips are then produced by laserscribing and breaking as shown in FIG. 5B. Specifically, the verticalscribe lines 190 and the horizontal scribe lines 192 may form a grid andthus show one exemplary manner for laser scribing and how eachindividual gain chip might be separated from the larger pattern or arrayof gain chips 180.

The surfaces of the heat spreader and the QW may have some resistanceand/or difficulty in forming a solid and complete optical bond dependingon the material compatibility. Adding a thin layer of dielectricmaterial such as CN or SiN to the surfaces of the heat spreader and theQW, may help alleviate the bonding resistance and help the surfaces ofthe heat spreader and QW bond. The thickness of the film must be chosenproperly to minimize optical reflectivity between the heat spreader andthe QW. FIG. 6 provides a graph that shows the reflectivity vs.thickness of the film with a refraction index of n=1.7. Accordingly, thebest choice for the thickness is 200 nm in this case.

FIG. 18A provides a schematic overview of a semiconductor including theconduction band 410 and valence band 412. A quantum well 414 is adepression in the semiconductor's valence and conduction bands. Oneimplementation hereof may include increasing the quantum efficiency of abarrier pumped laser 430. In a barrier-pumped laser 430, such as theschematic overview provided in FIG. 18B, pump photons 418 boost anelectron 416 from the valence band 412 of the bulk into the conductionband 410. In order to maximize the quantum efficiency in a barrierpumped laser, a QW hereof, is designed to absorb pump light as close as6% difference in the photon energy between the pumping wavelength andthe lasing wavelength. For example, in the developments hereof, oneimplementation uses 640 nm as pumping light to produce 680 nm light. Thedifference between 640 nm and 680 nm is approximately 6%, which bycomparison is significantly less than other laser designs which may use532 nm pumping wavelength to produce 680 nm lasing wavelength, which isapproximately a 28% difference between the photon energy between thepumping wavelength and the lasing wavelength.

In yet another implementation of the present developments hereof, thequantum efficiency may be further increased for in-well pumped lasers.In-well pumped lasers refers to the structure and methods utilized inlasers, in which the pump light is absorbed solely in the quantum wells.FIG. 18C provides an in-well-pumped laser 440, where the pump photon 418lifts an electron 416 from a level in the quantum well's valance band412 to the conduction band 410. In one implementation of thedevelopments hereof, the QW is designed to absorb light as close asapproximately 3% difference in the photon energy between the pumpingwavelength and the lasing wavelength. In one implementation, for in-wellpumped laser hereof, the pumping wavelength is 660 nm and the lasingwavelength is 680 nm. Furthermore, combining SiC contact cooling andin-well pumping together may maximize the generated visible light power.The in-well pumping structures, methods, and techniques may be known tothose skilled in the art, and are also disclosed in, severalpublications for example, “Direct Pumping of Quantum Wells ImprovesPerformance of Semiconductor Thin-Disk Lasers” Photonics Spectra (June2005) and “Enhanced Efficiency of AlGaInP Disk Laser by In-well Pumping”Optics Express, p. 2472 (2015).

FIG. 7 shows a schematic overview of an alternative implementation andarrangement of a MECSEL. In particular, FIG. 7 shows UV or VIS laser100, here a MECSEL 210 includes a MECSEL gain chip 250 that further hasone or more MECSEL quantum wells 220 (“QW” or “MECSEL QW”) which mayprovide the semiconductor gain media for the laser. Like the MECSELdescribed in FIG. 1A above, by enclosing the QW 220 inside a lasercavity, a few watts of visible light power can be extracted from thecavity by using one (or more) partial reflecting cavity mirror(s) 230.When electrically or optically pumped, the MECSEL QW 220 produces anoutput or VIS 140. Note that in this alternative implementation, that toeliminate that AR coating on the MECSEL's gain chip for VWL the MECSELgain chip 250 is placed at the Brewster angle θ_(B) (or a polarizationangle) relative to the optical path. The Brewster angle may help avoidsome amount of optical loss due to imperfect coating on the gain chip.

In one implementation of the current developments utilizing a highlymultimode operation may be included which may eliminate a feedback looprelated to power stability. The STDL has a bandwidth larger than severalnm which contains multiple frequencies. The STDL may provide the stableVWLS at ˜1 nm of bandwidth. The bandwidth can be further controlled byadding a wavelength limiting optic such as a birefringent filter plate(BFP) depending on the bandwidth requirement. Using the above describedhighly multimode operation, this alternative implementation may be ableto provide temporally stable high intensity VWLS. This alternativefeature may allow the developments hereof to avoid the mode beatingproblem while also avoiding single mode operation which may result inpower instability due to the cavity length change with temperature.Moreover, by using a highly multimode operation, the implementationshereof may also be able to avoid a complicated feedback system tomaintain the power stability, which may be a desirable characteristicfor a UV laser.

The selection of the proper NLC to be used in a UV laser device hereofmay need to have specific properties and characteristics to produce thedesired UV light. These properties and characteristics, may include, butare not limited to: (1) transparent in the corresponding VWL and UVwavelengths; (2) a high non-linear coefficient; (3) a large band widthto support multiple frequencies simultaneously; and (4) a minimumwalk-off angle. Exemplar NLCs that provide the desired characteristicsmay include: (a) periodically poled crystal such as Lithium Tantalate(PPLT or PPSLT); and/or, (b) periodically poled LaBGeO₅ (PPLBGO). Forboth PPLT and PPLBGO, either first, second, or higher order can be used.

FIG. 8 provides a graph that demonstrates the relative intensity versusthe wavelength (bandwidth and UV conversion efficiency) for twoNon-Linear Crystals (NLCs) lengths under similar Visible WavelengthLaser Light Source (VWLS) conditions. FIG. 8 further demonstrates thatthat the NLC length must be chosen properly, and that the length of theNLC plays an important role in the preferred function of the UV laser.Longer crystals may provide higher conversion efficiency but limits theband width. Therefore, the bandwidth requirement places a limit on themaximum length of the NLC. A cavity length of 60 mm has mode spacing of2.5 GHz (˜0.004 nm at 680 nm). A 1.6 mm long PPSLT has 0.1 nm band widthof full width at half maxima (FWHM) which allows ˜25 frequencies tooscillate inside such a cavity. Thus, FIG. 8 demonstrates the bandwidthand UV conversion efficiency at two NLC lengths under similar VWLS powerdensity. Further, FIG. 9 provides a graph that demonstrates that the NLClength is governed by the bandwidth requirement of the FWHM as shown.

FIG. 10 provides a schematic overview of an exemplary UV laser 101, herea VECSEL 110. The VECSEL 110 includes a VECSEL gain chip 150 that hasone or more quantum wells 120 (“QW” or “VECSEL QW”) that may be thesemiconductor gain media for the laser. In this example, theelectrically or optically pumped semiconductor thin disk gain media, orgain chip, 150, also serves as a first cavity mirror. In FIG. 10, an NLC270 is placed between 120, 130 in the output or optical path 140, wherethe NLC serves to produce UV light as the output or VIS 140 passesthrough the NLC. The UV light then travels and passes through thepartial reflecting or specially coated UV transmitting cavity mirror130. The gain chip 150 contains an intra-cavity SiC heat spreader with athin layer of CN or SiN coating between the heat spreader and the GaAswafer as described inter alia.

FIG. 11 provides yet another schematic overview of an alternativeimplementation of a UV laser 101, here a VECSEL 110. In thisconfiguration, the NLC 270 is placed inside the cavity that contains aVECSEL gain chip 150 that has one or more quantum wells 120. In thisimplementation, a BFP 280 is placed in the output or optical path 140.In this implementation a first specialized mirror 132 is placed afterthe BFP in line with the optical path. The first specialized mirror 132is unique in that it has an inner surface coated to reflect on VWL andhigh transmission of UV to extract UV light. The first specializedmirror 132 is angled to reflect or direct the output or VIS 140 throughan NLC 270 and toward a second specialized mirror 134. The secondspecialized mirror 134 has an inner surface coated to reflect both VWLand UV wavelengths. The second specialized mirror 134 reflects the UVlaser output or beam 142 through the NLC 270 and back through the firstspecialized mirror 132. Thus, the UV light generated in both directions,the left bound one is reflected by the second cavity mirror 134 back tomerge with the right bound one as a single UV output 142. In this way, astable VECSEL based UV laser output 142 is achieved.

FIG. 12 provides yet another schematic overview of an alternativeimplementation of a UV laser 101 that utilizes a MECSEL 210. In thisimplementation, the NLC 270 is placed inside the cavity that contains aMECSEL gain chip 250 that has one or more quantum wells 220. In thisimplementation, a BFP 280 is placed in the output 140 or optical path140. A first mirror 132 is placed after the BFP but in line with theoptical path. The first specialized mirror 132 is unique in that it hasan inner surface coated to reflect on VWL and transmission of UV toextract UV light. The first specialized mirror 132 is angled to reflector direct the output or VIS 140 through an NLC 270 and toward a secondspecialized mirror 134. The second specialized mirror 134 has an innersurface coated to reflect both VWL and UV wavelengths. The secondspecialized mirror 134 reflects the UV laser output through the NLC 270and back through the first specialized mirror 132. Thus, the UV lightgenerated in both directions, the left bound one is reflected by thesecond cavity mirror 134 back to merge with the right bound one as asingle UV output 142. A third mirror 136 is placed behind the MECSEL'sgain chip 250 to reflect back the VWL. By using mirrors 136, 132, and134 together, a stable VIS cavity is achieved. In this way, a stableMECSEL based UV laser is achieved.

FIG. 13 provides a schematic overview of a walk-off compensated NLC inaccordance with at least some implementations of developments hereof. Awalk-off compensated NLC available from the crystal supplier may be usedto satisfy a minimum walk-off requirement. For example, FIG. 13 providesa pair of beta-Barium Boron Oxide (BBO) optics 300 with the same phasematching angle are arranged in the opposite direction to bring thedeviated beam (2ω) 310 back to center again. The spacing between thesetwo BBOs 300 can be reduced to zero or in optical contact.

FIG. 14 provides a UV laser 101, here a VECSEL 110. The VECSEL 110includes a VECSEL gain chip 150 that has one or more quantum wells 120(“QW” or “VECSEL QW”) which may provide the semiconductor gain media forthe laser. In this example, the electrically or optically pumpedsemiconductor thin disk gain media, or gain chip, 150, also serves as afirst cavity mirror. In FIG. 14, an NLC 270 is placed in the output oroptical path 140, where the NLC serves to produce UV light as the outputor VIS passes through the NLC. The UV light then travels and passesthrough the partial reflecting or specially coated (highly reflectiveVIS and highly transmissive UV) cavity mirror 130. The gain chip 150contains an intra-cavity SiC heat spreader with/without a thin layer ofCN or SiN coating between the heat spreader and the GaAs wafer asdescribed inter alia.

FIG. 15 provides a UV laser 101, here an in-well pumped MECSEL 400. TheMECSEL assembly 410 includes SiC heat spreaders 420 that may or may nothave CN or SiN film layers as described elsewhere in this disclosure.Pumping light optics 430, 432, 434 are positioned at select locationsaround the MECSEL to recycle the unabsorbed pump light back to MECSELfor multiple passes in the in-well pumping. By enclosing the in-wellpumped MECSEL 400 inside a laser cavity, a few watts of visible lightpower can be extracted from the cavity by using one (or more) cavitymirror(s) 230/440. An NLC 270 is positioned in the output 140, oroptical path 140, to convert VWL to stable UV light 142. A second cavitymirror is located at the opposite end of the cavity, as the first cavitymirror 442. Thus, FIG. 15 provides an in-well pumped MECSEL 400 wherethe MECSEL QW 220 is sandwiched between CTE compatible heat spreaders420 to support multi-frequency of high intensity VWL output 140. In thisimplementation, red light pumping 450 is used to pump the MECSEL QW 220.In FIG. 15, an NLC 270 such as PPLT/PPLST or PP-LBGO of appropriatelength may be utilized to convert the multi-frequency output 140, intostable UV light 142. Other variations and implementations, of such aconfiguration may be employed to create a stable UV light 142 as furtherdisclosed and described inter alia.

FIG. 16 provides schematic overview of an arrangement of a VECSEL thatmay provide and enable a wide range of UV power output through the useof additional optics. FIG. 16 provides a UV laser 101, here a VECSEL110. The VECSEL 110 includes a VECSEL gain chip 150 that has one or morequantum wells 120 (“QW” or “VECSEL QW”) which may be or provide thesemiconductor gain media for the laser. In this example, theelectrically or optically pumped semiconductor thin disk gain media, orgain chip, 150, also serves as a first cavity mirror. In FIG. 16, an NLC270 is placed in the output or optical path 140, where the NLC 270serves to produce UV light 142 as the output VIS passes through the NLC270. The UV light 142 then travels and passes through the partialreflecting or special coated (highly reflective VIS and highlytransmissive UV) cavity mirror, or end mirror 138. The gain chip 150contains an intra-cavity SiC heat spreader with/without a thin layer ofCN or SiN coating between the heat spreader and the GaAs wafer asdescribed inter alia. FIG. 16 also provides or includes a focusing lens290.

In FIG. 16, additional optics, such as a focusing lens 290 may beutilized to increase the power output of the UV laser. The focusing lens290 may have a focal length of F1. The end mirror 138 may have a radiusof curvature of R2. Also provided in FIG. 16 are distances: D1, D2, andD3; where, D1 represents the distance between the surface of the VECSELgain chip 150 and the focusing lens 290; D2 represents the distancebetween the focusing lens 290 and the NLC 270; and D3 represents thedistance between the NLC 270 and the end mirror 138. In one aspect, theUV power output may be adjusted by setting the F1/R2 to be equal toapproximately 1 and the value of D1/(D2+D3) to be equal to approximately2. In this manner, the laser may be operated at a wide range of powerlevels.

FIG. 17 provides yet another schematic overview of a UV laser 101, herean in-well pumped MECSEL 400. The MECSEL assembly 410 includes SiC heatspreaders 420 that may or may not have CN or SiN film layers asdescribed elsewhere in this disclosure. Pumping light optics 430, 432,434 are positioned at select locations around the MECSEL to recycleunabsorbed pump light for multiple passes. By enclosing the in-wellpumped MECSEL 400 inside a laser cavity, a few watts of visible lightpower can be extracted from the cavity by using one (or more) cavitymirror(s) 230/440. In this example, a wavelength selecting and limitingoptics 292 is positioned in the output or VIS 140, or optical path, toselect and limit the VWF output 140. A second cavity mirror 444 islocated at the opposite end of the cavity, as the first cavity mirror440. The VWF output 140 is reflected by the second cavity mirror throughan NLC 270 to convert the multi-frequency output or VWF to UV light 142.The UV light is generated in both directions and the left bound one isreflected by a third cavity mirror 134 back to merge with the rightbound one as a single UV output 142. Thus, FIG. 17 provides an in-wellpumped MECSEL 400 where the MECSEL QW 220 is sandwiched between CTEcompatible heat spreaders 420 to support multi-frequency of highintensity VWL output 140. In this implementation, red light pumping 450is used to pump the MECSEL QW 220. In FIG. 17, an NLC 270 such asPPLT/PPLST or PP-LBGO of appropriate length may be utilized to convertthe multi-frequency output VIS 140, to stable UV light 142. Othervariations and implementations, of such a configuration may be employedto create a stable UV light 142 as further disclosed and described interalia.

FIG. 19A shows an example of a barrier-pumped laser 500. In FIG. 19A, apump photon 502 is pumped into the barrier 504a of the conduction band510. The pumping of the pump photon 502 into the barrier 504 creates anelectron hole pair 520 a, 520 b in the barrier 505. The electron holepair 520 a, 520 b migrates (as indicated by dashed lines 522 a, 522 b)to one of the quantum wells 514 where it recombines to create a laserphoton 524.

FIG. 19B shows an example of an in-well pumped laser 600. In FIG. 19B, apump photon 602 is pumped into a well 614 of the conduction band 610.The pump photon 602 is absorbed in the quantum well 614, which createsan electron-hole pair 620 a, 620 b in the quantum well 614. Afterrelaxation (as indicated by dashed lines 622 a, 622 b) to the groundstate, it recombines into a laser photon 624. The difference in energybetween pump and laser photon, referred to as the quantum defect, isdeposited as heat in the heat spreaders, as described in FIGS. 1A, 1B,and 2, inter alia.

The above discussion is meant to be illustrative of the principles andvarious implementations of the present developments. Numerousvariations, ramifications, and modifications of the basic concept whichhave not been described may become apparent to those skilled in the artonce the above disclosure is fully appreciated. It is intended that allsuch ramifications and variations be included within the scope of theappended claims and their legal equivalents, and the scope of theinvention not be limited by the examples given, or the claims hereof.

1. A method, device or system as described herein.
 2. A method, deviceor system according to claim 1; including a UV laser comprising: a gainchip having one or more quantum wells or one or more quantum dots andone or more mirrors.
 3. A method, device or system according to claim 1or 2; further including one or more of: the one or more mirrors beinghighly reflective; the one or more quantum wells being semiconductorgain media for the laser; the gain chip having one or more lasercavities, and the one or more quantum wells being enclosed inside theone or more laser cavities; the gain chip having one or moresemiconductor thin disc laser cavities, and particularly a VECSEL cavityor a MECSEL cavity; and/or the one or more mirrors being disposed toextract light from the one or more cavities.
 4. A method, device orsystem according to any of claims 1-3; the one or more quantum wellsbeing one or more of: electrically pumped or optically pumped, includingfiber coupled diode lasers or free space diode lasers.
 5. A method,device or system according to any of claims 1-4; further including oneor more of: visible light power intensity of at least a factor of about10 or more than its power outside of the cavity mirrors; an enhancementfactor of between about 40 and about 100 when the one or more cavitymirrors are highly reflective; provision of sufficient visible highintensity light to provide the temporally stable high intensity visiblelight requisite for a UV laser.
 6. A method, device or system accordingto any of claims 1-5; the laser further being or including one or moreof: a VECSEL gain chip and a MECSEL gain chip.
 7. A method, device orsystem according to any of claims 1-6; the laser further being orincluding one or more of: a VECSEL; a VECSEL with a VECSEL setup withsaid one or more mirrors being at least one mirror being operativelydisposed relative to the gain chip; a MECSEL; and a MECSEL with a MECSELsetup with said one or more mirrors being at least two mirrors beingoperatively disposed disparately relative to the gain chip.
 8. A method,device or system according to any of claims 1-7; including a UV laserthat provides for the efficient and/or temporally stable generation ofUV light from or using one or both: A) a Visible Wavelength Laser LightSource (VWLS), by using a laser cavity supporting multiple frequenciesof VWLS; and B) using length optimized non-linear optics to double thevisible frequencies inside the laser cavity into UV light.
 9. A method,device or system according to any of claims 1-8; for or using one orboth of VECSEL and MECSEL lasers including one or both barrier-pumped orin-well pumped lasers.
 10. A method, device or system according to anyof claims 1-9; including one or more of: manufacturing gain chips foruse in the lasers, arrangements of lasers, and selection of propernon-linear crystal (NLC) for use in the device.
 11. A method, device orsystem according to any of claims 1-10; including one or more of: (A)temporally stable high intensity of visible light, and (B) a propernon-linear crystal, or periodically poled material to convert thevisible light into UV light.
 12. A method, device or system according toany of claims 1-11; including one or both a VECSEL gain chip or a MECSELgain chip; either or both the VECSEL gain chip or the MECSEL gain chiphaving: one or more quantum wells (“QW” or “VECSEL QW”) or quantum dots(“QD”).
 13. A method, device or system according to any of claims 1-12;the VECSEL gain chip or the MECSEL gain chip being a semiconductor gainmedia for the laser.
 14. A method, device or system according to any ofclaims 1-13; comprising one or more of: enclosing the QW or QD inside alaser cavity: extracting a few watts of visible light power from thecavity by using one or more partial reflecting cavity mirrors;electrically or optically pumping, the VECSEL QW or QD or MECSEL QW orQD producing an output; between the cavity mirrors, the visible lightpower intensity may be at least a factor of 10 or more than its poweroutside of the cavity mirrors; the enhancement factor being betweenabout 40 and about 100 when all cavity mirrors are highly reflective; asemiconductor thin disc laser cavity, and particularly a VECSEL cavityor MECSEL providing the necessary visible high intensity light toprovide temporally stable high intensity visible light for a UV laser.15. A method, device or system according to any of claims 1-14;including one or more non-linear crystals (NLCs) for use in the device.16. A method, device or system according to claims 1-15; comprising oneor more of: cooling for high power operation; a gain region of both theVECSEL gain chip and a MECSEL gain chip having one or both a layeredstructure or layered arrangement for cooling; and, one or more of heatspreaders and reflectors layered, or sandwiched, around the QWstructure.
 17. A method, device or system according to any of claims1-16; including one or more of the gain chip comprising: a heat spreaderas the first layer thereof; a heat spreader as the first layer thereof,the heat spreader being of a material or composition selected fromdiamond, SiC, GaAs, or a high-thermal conducting optic material for acooling layer; a second layer being or including the one or more quantumwells or quantum dots; and/or a third layer being or including adistributed bragg reflector (DBR).
 18. A method, device or systemaccording to claim 17; the gain chip further being one of: a VECSEL gainchip and a MECSEL gain chip.
 19. A method, device or system according toclaim 18; the gain chip further being a MECSEL gain chip and one or moreof: the MECSEL gain chip having one or more additional heat spreaders;the MECSEL gain chip sandwiching the MECSEL QW structure between twocooling devices, or heat spreaders and, the MECSEL gain chip having noDBR structure.
 20. A method, device or system according to any of claims1-19; comprising one or more of: a method of producing a VECSEL gainchip or a MECSEL gain chip, where the QW or QD structure is firstgrowing the QW or QD structure on a desired substrate, or wafer, such asGaAs; a substrate typically having a thickness of 0.2-0.5 mm dependingon the wafer diameter. optically bonding a heat spreader such as SiC tothe QW-GaAs wafer; the optical bonding including conforming one wafer toanother wafer to maintain good optical and thermal contact.
 21. Amethod, device or system according to any of claims 1-20; comprising oneor more of: making the QW-GaAs or QD-GaAs wafer more flexible; reducingthe QW-GaAs or QD-GaAs wafer thickness from the GaAs side to around 0.1mm or less; surface activating the SiC wafer and the thin, or reducedthickness, QW-GaAs or QD-GaAs wafer; bonding or pressing together theSiC wafer and the thin, or reduced thickness, QW-GaAs or QD-GaAs waferin an optical bonding machine; bonding or pressing together the SiCwafer and the thin, or reduced thickness, QW-GaAs or QD-GaAs wafer in anoptical bonding machine under ultra-high vacuum conditions; and theVECSEL gain chip terminated by a DBR.
 22. A method, device or systemaccording to any of claims 1-21; comprising one or more of: making,according to one or more of claims 1-21, the SiC-QW-GaAs or SiC-QD-GaAsinto a single wafer of partial MECSEL QW wafer assembly; dipping apartial MECSEL QW wafer assembly into acid solution such asH₂SO₄:H₂O₂:H₂O, or concentrated sulfuric acid, or NH₄OH:H₂O₂ etchant toremove the GaAs selectively; following this acid wash, only the thin QWor QD layer is left on the SiC wafer; activating a second SiC wafer andpressing the second SiC wafer to the SiC-QW or SiC-QD, utilizing thebonding process in a standard optical bonding machine under high orultra-high vacuum conditions; resulting in the formation of a singleSiC-QW-SiC or SiC-QD-SiC wafer.
 23. A method, device or system accordingto any of claims 1-22; comprising one or more of: further processing theSiC-QW-GaAs or SiC-QD-GaAs (VECSEL) wafer and the SiC-QW-SiC orSiC-QD-SiC (MECSEL) wafer by applying an anti-reflection (AR) coatingand metallization with a pattern; and, producing one or both of asingle, or individual, SiC-QW-GaAs or SiC-QD-GaAs (VECSEL) gain chip,and a single, or individual, SiC-QW-SiC or SiC-QD-SiC (MECSEL) gain chipby laser scribing and breaking.
 24. A method, device or system accordingto any of claims 1-23; comprising one or more of: laser scribing byforming a grid of vertical scribe lines and horizontal scribe lines andseparating how each individual gain chip from a larger pattern or arrayof gain chips.
 25. A method, device or system according to any of claims1-24; comprising one or more of: adding a thin layer of dielectricmaterial such as CN or SiN to the surfaces of the heat spreader and theQW or QD, adding a thin layer of dielectric material such as CN or SiNto the surfaces of the heat spreader and the QW to alleviate the bondingresistance and help the surfaces of the heat spreader and QW bond; thesurfaces of the heat spreader and the QW may have some resistance and/ordifficulty in forming a solid and complete optical bond depending on thematerial compatibility; choosing the thickness of the film to minimizeoptical reflectivity between the heat spreader and the QW or QD;choosing the thickness of the film to minimize optical reflectivitybetween the heat spreader and the QW for the reflectivity vs. thicknessof the film to have a refraction index of n=1.7; choosing the thicknessof the film to minimize optical reflectivity between the heat spreaderand the QW, the thickness being about 200 nm.
 26. A method, device orsystem according to any of claims 1-25; comprising one or more of: asemiconductor including a conduction band and a valence band.
 27. Amethod, device or system according to any of claims 1-26; comprising oneor more of: a quantum well being a depression in one or both the valenceand conduction bands; increasing the quantum efficiency of a barrierpumped laser by pumping photons; boosting an electron from the valenceband of the bulk into the conduction band; maximizing the quantumefficiency in a barrier pumped laser, a QW hereof, absorbing pump lightas close as about 6% difference in the photon energy between the pumpingwavelength and the lasing wavelength; using 640 nm as pumping light toproduce 680 nm light; using a difference between 640 nm and 680 nm beingapproximately 6%.
 28. A method, device or system according to any ofclaims 1-27; comprising one or more of: increasing the quantumefficiency for in-well pumped lasers; increasing the quantum efficiencyfor in-well pumped lasers; in which the pump light is absorbed solely inthe quantum wells; increasing the quantum efficiency for in-well pumpedlasers; where the pump photon lifts an electron from a level in thequantum well's valance band to the conduction band; increasing thequantum efficiency for in-well pumped lasers; where the pump photonlifts an electron from a level in the quantum well's valance band to theconduction band, the QW absorbing light as close as approximately 3%difference in the photon energy between the pumping wavelength and thelasing wavelength increasing the quantum efficiency for in-well pumpedlasers; where the pump photon lifts an electron from a level in thequantum well's valance band to the conduction band; for in-well pumpedlaser hereof, the pumping wavelength is 660 nm and the lasing wavelengthis 680 nm; increasing the quantum efficiency for in-well pumped lasers;where the pump photon lifts an electron from a level in the quantumwell's valance band to the conduction band, maximizing the generatedvisible light power by combining SiC contact cooling and in-wellpumping.
 29. A method, device or system according to any of claims 1-28;a barrier-pumped laser comprising one or more of: a pump photon pumpedinto a barrier of a conduction band; the pumping of the pump photon intothe barrier creating an electron hole pair in the barrier; the electronhole pair migrating to one of the one or more quantum wells recombiningto create a laser photon.
 30. A method, device or system according toany of claims 1-28; an in-well pumped laser comprising one or more of: apump photon pumped into a well of a conduction band; the pump photonbeing absorbed in one of the one or more quantum wells, creating anelectron-hole pair in the quantum well, relaxing to a ground state,recombining into a laser photon; the difference in energy between pumpand laser photon, the quantum defect, being deposited as heat in theheat spreaders.
 31. A method, device or system according to any ofclaims 1-30; a UV laser comprising one or more of: a MECSEL including aMECSEL gain chip that further has one or more MECSEL quantum wells,placing the MECSEL gain chip at the Brewster angle θ_(B) or thepolarization angle relative to the optical path; a MECSEL gain chip thatfurther has one or more MECSEL quantum wells, placing the MECSEL gainchip at the Brewster angle θ_(B) or the polarization angle relative tothe optical path to eliminate an AR coating on the MECSEL's gain chipfor Visible Wavelength Laser Light Source; a MECSEL gain chip thatfurther has one or more MECSEL quantum wells, placing the MECSEL gainchip at the Brewster angle θ_(B) or the polarization angle relative tothe optical path, the Brewster angle reducing optical loss due toimperfect coating on the gain chip.
 32. A method, device or systemaccording to any of claims 1-31; a UV laser comprising one or more of: aVECSEL gain chip having one or more quantum wells (“QW” or “VECSEL QW”or QD) being the semiconductor gain media for the laser; the VECSEL gainchip being an electrically or optically pumped semiconductor thin diskgain media, that is also a first cavity mirror; an NLC placed in theoutput or optical path, the NLC producing UV light as the output passesthrough the NLC; the UV light then traveling and passing through apartial reflecting cavity mirror; the gain chip containing anintra-cavity SiC heat spreader with a thin layer of CN or SiN coatingbetween the heat spreader and the GaAs wafer.
 33. A method, device orsystem according to any of claims 1-32; a UV laser comprising one ormore of: a VECSEL with a cavity that contains a VECSEL gain chip thathas one or more quantum wells and an NLC placed inside the cavity; and aBFP placed in the output or optical path, and a first specialized mirrorplaced after the BFP in line with the optical path; the firstspecialized mirror having an inner surface coated to reflect on VWL andhigh transmission of UV to extract UV light; the first specializedmirror being angled to reflect the output through an NLC and toward asecond specialized mirror; the second specialized mirror having an innersurface coated to reflect both VWL and UV wavelengths; and the secondspecialized mirror reflecting the UV laser output through the NLC andback through the first specialized mirror.
 34. A method, device orsystem according to any of claims 1-33; a UV laser comprising one ormore of: a MECSEL a with a cavity that contains a MECSEL gain chip thathas one or more quantum wells and an NLC placed inside the cavity; and aBFP placed in the output or optical path; and a first mirror placedafter the BFP in line with the optical path; the first mirror beingspecialized and having an inner surface coated to reflect on VWL andtransmission of UV to extract UV light; the first specialized mirrorbeing angled to reflect the output through the NLC and toward a secondspecialized mirror; the second specialized mirror having an innersurface coated to reflect both VWL and UV wavelengths; and the secondspecialized mirror reflecting the UV laser output through the NLC andback through the first specialized mirror; a third mirror placed behindthe MECSEL's gain chip to reflect back the VWL.
 35. A method, device orsystem according to any of claims 1-34; a UV laser comprising one ormore of: a VECSEL including a VECSEL gain chip that has one or morequantum wells (“QW” or “VECSEL QW” or QD) providing electrically oroptically pumped semiconductor gain media for the laser; thesemiconductor thin disk gain media, or gain chip, also serving as afirst cavity mirror; an NLC placed in the output or optical path, theNLC producing UV light as the output passes through the NLC, the UVlight then traveling and passing through the partial reflecting cavitymirror; the gain chip containing an intra-cavity SiC heat spreader witha thin layer of CN or SiN coating between the heat spreader and the GaAswafer.
 36. A method, device or system according to any of claims 1-35; aUV laser comprising one or more of: an in-well pumped MECSEL including aMECSEL assembly, the MECSEL assembly including one or more SiC heatspreaders that may optionally have CN or SiN film layers; pumping lightoptics positioned around the MECSEL to assist in in-well pumping; alaser cavity enclosing the in-well pumped MECSEL therewithin inside thelaser cavity, providing for extracting a few watts of visible lightpower from the cavity by using one or more cavity mirrors; an NLCpositioned in the output or optical path to convert VWL to stable UVlight; a second cavity mirror located at the opposite end of the cavity,as the first cavity mirror; providing an in-well pumped MECSEL where theMECSEL QW is sandwiched between CTE compatible heat spreaders to supportmulti-frequency of high intensity VWL output; red light pumping to pumpthe MECSEL QW; an NLC PPLT/PPLST or PP-LBGO of appropriate lengthutilized to convert the multi-frequency output to stable UV light.
 37. Amethod, device or system according to any of claims 1-36; a UV lasercomprising one or more of: an arrangement of a VECSEL that provides awide range of UV power output through the use of additional optics;providing a VECSEL including a VECSEL gain chip that has one or morequantum wells (“QW” or “VECSEL QW” or QD) providing electrically oroptically pumped semiconductor gain media for the laser; theelectrically or optically pumped semiconductor thin disk gain media, orgain chip also serving as a first cavity mirror; an NLC placed in theoutput or optical path the NLC serving to produce UV light as the outputpasses through the NLC, the UV light then traveling and passing throughthe partial reflecting cavity mirror, or end mirror; the gain chipcontaining an intra-cavity SiC heat spreader with a thin layer of CN orSiN coating between the heat spreader and the GaAs wafer; providing afocusing lens.
 38. A method, device or system according to any of claims1-37; a UV laser comprising one or more of: additional elements toincrease the power output of the UV laser; additional optics and/or afocusing lens.
 39. A method, device or system according to any of claims1-38; a UV laser comprising one or more of: a focusing lens having afocal length of F1; an end mirror having a radius of curvature of R2;distances: D1, D2, and D3; D1 representing the distance between thesurface of the gain chip and the focusing lens; D2 representing thedistance between the focusing lens and an NLC; and D3 representing thedistance between the NLC and the end mirror.
 40. A method, device orsystem according to claim 39; a UV laser comprising one or more of:operating the laser may be operated at a wide range of power levels;operating the laser may be operated at a wide range of power levels byadjusting the UV power output by setting the F1/R2 to be equal toapproximately 1 and the value of D1/(D2+D3) to be equal to approximately2.
 41. A method, device or system according to any of claims 1-40; a UVlaser comprising one or more of: an in-well pumped MECSEL including aMECSEL assembly comprising: one or more SiC heat spreaders optionallyhaving CN or SiN film layers; pumping light optics positioned around theMECSEL for in-well pumping; extracting visible light power by enclosingthe in-well pumped MECSEL inside a laser cavity, the extracting from thecavity by using one or more cavity mirrors. positioning wavelengthselecting and limiting optics in the output or optical path, to selectand limit the VWF output.
 42. A method, device or system according toany of claims 1-41; a UV laser comprising one or more of: a secondcavity mirror located at the opposite end of the cavity, relative to thefirst cavity mirror; reflecting VWF output a second cavity mirrorthrough an NLC to convert the multi-frequency output to UV light;reflecting UV light by a third cavity mirror back as a UV output;providing an in-well pumped MECSEL where the one or more MECSEL QW or QDare sandwiched between CTE compatible heat spreaders to supportmulti-frequency of high intensity VWL output; red light pumping to pumpthe one or more MECSEL QW or QD; NLC being one or more of PPLT/PPLST orPP-LBGO of appropriate length to convert the multi-frequency output tostable UV light.
 43. A method, device or system according to any ofclaims 1-42; a UV laser comprising one or more of: utilizing a highlymultimode operation to eliminate a feedback loop related to powerstability; an STDL having a bandwidth larger than several nm whichcontains multiple frequencies; an STDL providing a stable VWLS at ˜1 nmof bandwidth; controlling bandwidth by adding a wavelength limitingoptics such as a birefringent filter plate (BFP) depending on thebandwidth requirement; using highly multimode operation to providetemporally stable high intensity VWLS; to avoid the mode beating problemwhile also avoiding single mode operation resulting in power instabilitydue to the cavity length change with temperature; using a highlymultimode operation to avoid a complicated feedback system to maintainthe power stability.
 44. A method, device or system according to any ofclaims 1-43; a UV laser comprising one or more of: selecting a properNLC to be used in a UV laser device; selecting a proper NLC to be usedin a UV laser device having one or more of: (1) transparency in thecorresponding VWL and UV wavelengths; (2) a high non-linear coefficient;(3) a large band width to support multiple frequencies simultaneously;and (4) a minimum walk-off angle. selecting a proper NLC to be used in aUV laser device including one or more of: an exemplar NLC providing onor more of: (a) periodically poled crystal such as Lithium Tantalate(PPLT or PPSLT); and/or, (b) periodically poled LaBGeO₅ (PPLBGO); forboth PPLT and PPLBGO, either first, second, or higher order can be used;selecting a proper NLC to be used in a UV laser device; one or more of:the bandwidth requirement placing a limit on the maximum length of theNLC; a cavity length of 60 mm having mode spacing of 2.5 GHz (˜0.004 nmat 680 nm); a 1.6 mm long PPSLT having 0.1 nm band width of full widthat half maxima (FWHM) which allows ˜25 frequencies to oscillate insidesuch a cavity; a bandwidth and UV conversion efficiency at two NLClengths under similar VWLS power density; an NLC length that is governedby the bandwidth requirement of the FWHM.
 45. A method, device or systemaccording to any of claims 1-44; a UV laser comprising one or more of: awalk-off compensated NLC to satisfy a minimum walk-off requirement; apair of beta-Barium Boron Oxide (BBO) optics with substantially same orsimilar phase matching angles arranged in the opposite direction tobring a deviated beam (2w) back to center again; reducing spacingbetween these two BBOs to about zero or in optical contact.
 46. Amethod, device, or system according to claims 1-45, comprising: acavity; at least one external energy source configured to provideelectrical or optical pumping energy; a semiconductor thin disc gainmedia enclosed within the cavity having one or more quantum wellsconfigured to receive and transform electrical or optical pumping energyfrom the external energy source and produce multi-frequency highintensity visible wavelength laser light; a heat spreader; a non-linearcrystal configured to convert the visible wavelength light toultra-violet light; and one or more mirrors.
 47. A method, device, orsystem according to claims 1-46, wherein the external energy source isred optical light.
 48. A method, device, or system according to claims1-47, wherein the semiconductor thin disc gain media further comprises acavity mirror.
 49. A method, device, or system according to claims 1-48,wherein a thin layer of CN or SiN is layered between the heat spreaderand the quantum wells.
 50. A method device, or system according toclaims 1-49, wherein one mirror is disposed opposite of thesemiconductor thin disc gain media.
 51. A method, device, or systemaccording to claims 1-50, wherein the mirror that is disposed oppositeof the semiconductor thin disc gain media has an inner surface with ahigh reflection coating for visible wavelength light and hightransmission for ultra-violet light.
 52. A method, device, or systemaccording to claims 1-51, comprising: a cavity; at least one externalenergy source configured to provide electrical or optical pumpingenergy; a semiconductor thin disc gain media enclosed within the cavityhaving one or more quantum wells configured to receive and transformelectrical or optical pumping energy from the external energy source andproduce multi-frequency high intensity visible wavelength laser light; aheat spreader; a non-linear crystal configured to convert the visiblewavelength light to ultra-violet light; and one or more mirrors.
 53. Amethod, device, or system according to claims 1-52, wherein the thindisc gain media is selected from either a MECSEL or a VECSEL.
 54. Amethod, device, or system according to claims 1-53, wherein the MECSELor VECSEL is stimulated by either barrier pumping or in-well pumping.55. A method, device, or system according to claims 1-54, wherein thenon-linear crystal is selected from the group of periodically poledlithium tantalite, periodically poled stoichiometric lithium tantalite,and periodically poled LaBGeO₅.
 56. A method, device, or systemaccording to claims 1-55, further comprising pumping light opticsarranged in the cavity to increase the intensity of the pumped lightfrom the external source.
 57. A method, device, or system according toclaims 1-56, further comprising a focus lens.
 58. A method, device, orsystem according to claims 1-57, further comprising selecting a focuslens having a focal length of F1, selecting an end mirror having aradius of curvature of R2, wherein F1/R2 is equal to approximately 1.59. A method, device, or system according to claims 1-58, furthercomprising arranging the distance between the surface of the VECSEL orMECSEL gain chip and the focusing lens to be D1; arranging the distancebetween the focusing lens and the NLC to be D2; and arranging thedistance between the NLC and the end mirror to be D3, so that the valueof D1/(D2+D3) is equal to approximately 2.